Switch to included line rental?

I'm currently on Unlimited Fibre Extra (switched from the lower speed Fibre in August) and paying £37.98 (£19.99 broadband + £17.99 line rental after the increase. Line is also supplied by PlusNet). I've just noticed that Unlimited Fibre Extra is now being advertised at £32.50 with the line rental included so obviously not happy with having to pay over £5/mo more on my current arrangement for seemingly the same thing.

Is there any way I can go about switching to the current price where the line rental is included?